1. Field of the Invention
The present invention relates to a production apparatus of expansion-molded articles, and particularly to a production apparatus of expansion-molded articles, which has been designed to effectively enhance the ability to fill foamed particles into a mold. The present invention also relates to an auxiliary member for transfer of foamed particles used in the production apparatus of expansion-molded articles. The present invention is further concerned with a method for producing an expansion-molded article using this apparatus.
2. Description of the Background Art
As methods of transferring foamed particles stored in a hopper to a mold and filling them into the mold upon molding of the foamed particles in the mold, there have heretofore been known the following methods:
(1) a method in which a mold is evacuated upon filling to set up an air current, and foamed particles are transferred to and filled into the mold by the air current (Japanese Patent Application Laid-Open No. 43762/1988);
(2) a method in which compressed air is ejected from a compressed-air ejection nozzle of a foamed particle feeder installed on a mold to set up an air current, and foamed particles are transferred to and filled into the mold by the air current (Japanese Patent Application Laid-Open Nos. 43762/1988, 46623/1987 and 77331/1993); and
(3) a method in which foamed particles within a hopper are kept under pressure to set up an air current by using the pressure within the hopper and the method (2) in combination, and the foamed particles are transferred to and filled into the mold by the air current (Japanese Patent Application Laid-Open Nos. 176747/1985, 79625/1986 and 87327/1987, and Japanese Patent Publication No. 87364/1993).
However, only a differential pressure of 1 atm can be obtained at the most by the method (1). Therefore, the foamed particles have been unable to be filled at a high filling density into the mold. The method (1) has hence involved a problem that the resulting expansion-molded article tends to have poor interparticle fusion bonding or high shrinkage factor, and so percent defective increases. In addition, according to this method, it has also been difficult to conduct blow back of excess foamed particles not filled into the mold into the hopper.
If the blow back of the foamed particles is only incompletely carried out, there is a possibility that the foamed particles may remain in a space defined in the rear of a piston for closing a foamed particle introducing opening in the mold while the piston is being moved forward, and so the backward movement of the piston may be blocked by the foamed particles remained in the space defined in the rear of the piston, resulting in a failure to fully fill new foamed particles into the mold upon the next molding.
The method (2) permits the filling of the foamed particles at a higher filling density than the method (1). However, the method (2) has involved a problem that if the form of a mold cavity becomes somewhat complicated, a failure in filling of the foamed particles occurs, and consequently many of the resulting expansion-molded articles tend to have poor interparticle fusion bonding or high shrinkage factor, and so percent defective increases.
The failure in filling of the foamed particles caused by the complicated cavity form may be improved to some extent by installing an additional feeder in the mold. In order to install the additional feeder, however, it is necessary to newly make an additional hole for installing the feeder in the mold. However, the installation of the additional feeder involves undesirable problems that the strength of the mold may possibly be markedly deteriorated according to the position of the hole for installing the new feeder, and the installation of more feeders increases the number of marks of the tip form of the feeder transferred to the surface of the resulting expansion-molded article to deteriorate the external appearance of the expansion-molded article. In some cases, it has been impossible in itself to install the additional feeder. Namely, the position where the feeder is intended to install is a position corresponding to the surface of the resulting molded article on which the transferred mark should not be left, or in some cases the additional feeder may not be installed due to the presence of piping and the like in the machine. After all, the installation of the additional feeder cannot be a preferable means for solution.
The method (3) has involved a problem that since the foamed particles kept under pressure in the hopper are exposed to a pressure lower than the pressure within the hopper upon their filling, the foamed particles undergo volume expansion within the hopper, at the outlet of the hopper, or within a pipe, and the expanded foamed particles tend to clog the outlet or the pipe and the like. The clogging of the outlet or the pipe and the like with the foamed particles has offered a problem that a failure in filling of the foamed particles into the mold occurs. There has also been involved a problem that since the interior of the hopper is pressurized, blow back of excess foamed particles into the hopper cannot be effectively carried out.
The present invention has been completed in view of the foregoing circumstances, and has as its object the provision of a production apparatus of expansion-molded articles, which can solve the above-described drawbacks and certainly reduce defective molding attendant on a failure in filling.
Another object of the present invention is to provide an auxiliary member for transfer of foamed particles, which permits effective filling of the foamed particles into the production apparatus of expansion-molded articles.
A further object of the present invention is to provide a method for producing an expansion-molded article using the above production apparatus of expansion-molded articles.
According to the present invention, there is thus provided a production apparatus of expansion-molded articles, comprising a mold equipped with a feeder for filling foamed particles into the mold having a through-hole through which the foamed particles can pass and a compressed-air ejection nozzle opening toward the mold, by which foamed particles contained in a hopper is filled into the mold through the through-hole of the feeder by ejecting compressed air from the compressed-air ejection nozzle and then heated to expand them, and the foamed particles thus expanded are then cooled, thereby producing an expansion-molded article, wherein the apparatus is equipped with a compressed-air discharge orifice opening toward the foamed particle filling side of the apparatus in the course of a foamed-particle supply line connecting the hopper to the inlet of the feeder.
The compressed-air discharge orifice in the production apparatus according to the present invention may be formed by joining an auxiliary member for transfer of foamed particles, which comprises a through-hole through which the foamed particles can pass, and a vent hole communicating with the through-hole and having an opening which opens within the through-hole in such a manner that the compressed air can be fed in one direction extending from the through-hole, to a foamed-particle transfer pipe on a foamed-particle supply line connecting the hopper to the inlet of the feeder, so as to direct the compressed air fed through the opening to the side of the feeder. The compressed-air discharge orifice may preferably be provided near an outlet of the hopper. A plurality of the compressed-air discharge orifices may be formed in the course of the foamed-particle supply line connecting the hopper to the inlet of the feeder. It may also be preferable that the open edge on the hopper side of the compressed-air discharge orifice, and the vicinity thereof may be formed in a shape smoothly curved from the vicinity of the open edge to the open edge in a peripheral direction of the foamed-particle supply line.
According to the present invention, there is also provided an auxiliary member for transfer of foamed particles, which comprises a through-hole through which the foamed particles can pass, and a vent hole communicating with the through-hole and adapted to feed compressed air for assisting the transfer of the foamed particles within the through-hole to the through-hole, wherein an opening of the vent hole defined within the through-hole opens in such a manner that the compressed air can be fed in one direction extending from the through-hole.
A compressed-air discharge orifice defined by the opening of the vent hole in the auxiliary member may preferably be such that its open edge on the hopper side and the vicinity thereof are formed in a shape smoothly curved from the vicinity of the open edge to the open edge in a peripheral direction of the auxiliary member for transfer of foamed particles supply line.
According to the present invention, there is further provided a method for producing an expansion-molded article by using a mold equipped with a feeder for filling foamed particles into the mold having a through-hole through which foamed particles can pass and a compressed-air ejection nozzle opening toward the mold, ejecting compressed air from the compressed-air ejection nozzle for a predetermined period of time to fill the foamed particles contained in a hopper into the mold through the feeder, moving a piston of the feeder forward while continuously ejecting the compressed air from the compressed-air ejection nozzle, so as to close a foamed particle introducing opening in the mold, heating the foamed particles filled into the mold to expand them and then cooling the foamed particles thus expanded, wherein upon the filling of the foamed particles, compressed air is fed toward the foamed particle filling side from a compressed-air discharge orifice provided in the course of a foamed-particle supply line connecting the hopper to the inlet of the feeder.
In the production method according to the present invention, the feed of the compressed air from the compressed-air discharge orifice to the foamed-particle supply line may preferably be begun at the time the compressed air is ejected from the compressed-air ejection nozzle, or the time the feed of the compressed air for ejecting the compressed air is started, and terminate at the same time as the time the forward movement of the piston of the feeder is started, or before that, and particularly may preferably be begun at the time the compressed air is ejected from the compressed-air ejection nozzle, or the time the feed of the compressed air for ejecting the compressed air is started, and terminated right before the forward movement of the piston of the feeder is started. The pressure of the compressed air ejected from the compressed-air ejection nozzle may preferably be kept at 1 to 10 kg/cm2G, and the pressure of the compressed air discharged from the compressed-air discharge orifice may preferably be kept at 30 to 95% of the pressure of the compressed air ejected from the compressed-air ejection nozzle.
The above and other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood from the preferred embodiments of the present invention, which will be described subsequently in detail with reference to the accompanying drawings, and from the appended claims.